1. Field of the Invention
The present invention relates in general to integrated circuit (IC) probes and in particular to a self-soldering probe assembly that attaches a set of probes to input/output pins of a flat pack IC package.
2. Description of Related Art
When testing a circuit implemented by integrated circuits (ICs) mounted on a circuit board, a technician can access a circuit node by manually holding a probe to a pin of an IC. However it is difficult for a technician to concurrently access more than one or two IC pins using this method. It is also often difficult to access pins of an IC mounted on a circuit board when the circuit board is in its normal operating environment. For example when the circuit board is installed in a backplane next to another circuit board there can be very little clearance between the circuit boards for accommodating a probe. Thus it would be beneficial to provide a probe that can be firmly connected to an IC mounted on a circuit board, that would remain attached when the circuit board is thereafter installed in its normal operating environment, and which has a low profile so that it requires very little space above the IC.
Probes have been developed which clamp to IC pins. For example U.S. Pat. No. 4,767,985 issued Aug. 30, 1988 to Shearer, Jr. et al describes a probe that clamps to the corner pins of an IC package. Such a probe is suitable for packages having pins that can be easily gripped by a probe. However flat pack IC packages having pins that are soldered flush with the circuit board would be difficult for such a probe to firmly grip. Also the described probe assembly is relatively tall and would not be useful where space above the IC is limited.
U.S. Pat. No. 4,362,991 issued Dec. 7, 1982 to Carbine describes a probe assembly for flat pack IC packages employing an external frame to hold a probe onto flat pack pins by pressure. However the assembly is large and inconvenient to use insofar as the circuit board has to be mounted within the probe assembly rather than installed in its normal operating environment.
U.S. Pat. No. 4,055,800 issued Oct. 25, 1977 to Fisk et al. describes a probe that clamps to the body of an IC rather than to its pins. While this type of probe can grasp relatively thick integrated circuit packages, a flat pack package is typically so thin that it would be difficult for such a probe to firmly grip its body. Also since the probe is held to an IC package body only by lateral pressure, it can easily fall off. This probe assembly is also relatively tall and therefore not practical where space above the IC is limited.
What is needed is a probe assembly for easily and firmly holding a set of probes onto pins of a flat pack or other type of integrated circuit package mounted on a circuit board and which has a relatively low profile so that it does not require substantial space above the circuit board.
It would also be desirable to provide a low profile probe assembly that can access a large number of IC pins. However such a probe assembly would require a large number conductors to convey signals between the probe assembly and external test equipment requiring access to the IC pins. It would therefore also be helpful if the probe assembly itself could carry out some of the functions of the external test equipment so as to reduce the number of connections between the probe assembly and the external test equipment.
It would be of further benefit for a probe assembly to provide a relatively short signal path between an IC pin and high impedance buffer amplifier. Prior art probes typically include high-impedance buffer amplifiers in the signal path between an IC pin and test equipment accessing the pin in order to reduce the load the probe presents at the pin. However, since prior art probe assemblies provide a relatively long signal path between an IC pin and buffer amplifier, the capacitance and inductance of those signal paths act as a load on the IC pin. By providing a very short path between buffer amplifiers and the IC pins, an improved probe assembly would reduce the load on the IC pins.